From 9e80ad4c23a8e604d6e459d35c80efc8af17b584 Mon Sep 17 00:00:00 2001
From: Luna <git@l4.pm>
Date: Tue, 24 Sep 2019 18:49:35 -0300
Subject: [PATCH] fix if statement emitting

 - don't emit br instructions (or any other) if branch emits ret
 - remove phi node (ifs are statements, not exprs)

 - emit to testfile (even if ir is broken)
---
 src/codegen.zig | 67 ++++++++++++++++++++++++++++++++++++-------------
 src/parsers.zig |  1 +
 2 files changed, 51 insertions(+), 17 deletions(-)

diff --git a/src/codegen.zig b/src/codegen.zig
index f28943a..b45d355 100644
--- a/src/codegen.zig
+++ b/src/codegen.zig
@@ -114,11 +114,10 @@ pub const Codegen = struct {
 
                 var insert = llvm.LLVMGetInsertBlock(builder);
                 var function = llvm.LLVMGetBasicBlockParent(insert);
-                var global_ctx = llvm.LLVMGetGlobalContext();
 
                 var then_bb = llvm.LLVMAppendBasicBlock(function, c"then");
-                var else_bb = llvm.LLVMCreateBasicBlockInContext(global_ctx, c"else");
-                var merge_bb = llvm.LLVMCreateBasicBlockInContext(global_ctx, c"ifcont");
+                var else_bb = llvm.LLVMAppendBasicBlock(function, c"else");
+                var merge_bb = llvm.LLVMAppendBasicBlock(function, c"ifcont");
 
                 var condbr = llvm.LLVMBuildCondBr(builder, icmp, then_bb, else_bb);
 
@@ -126,11 +125,27 @@ pub const Codegen = struct {
 
                 // roughly translating to kaleidoscope's
                 // 'Value *ThenV = Then->codegen();'
+                var then_rets = false;
+                var else_rets = false;
+
                 for (ifstmt.then_branch.toSlice()) |then_stmt| {
-                    try self.emitStmt(builder, &then_stmt);
+
+                    // keep emitting until branch has ret
+                    if (!then_rets)
+                        try self.emitStmt(builder, &then_stmt);
+
+                    switch (then_stmt) {
+                        .Return => then_rets = true,
+                        else => {},
+                    }
                 }
 
-                _ = llvm.LLVMBuildBr(builder, merge_bb);
+                // only build the br instruction if we didn't ret, because
+                // there can't be any instruction after a terminator
+                // same applies for the else branch
+                if (!then_rets)
+                    _ = llvm.LLVMBuildBr(builder, merge_bb);
+
                 then_bb = llvm.LLVMGetInsertBlock(builder);
 
                 llvm.LLVMPositionBuilderAtEnd(builder, else_bb);
@@ -139,22 +154,34 @@ pub const Codegen = struct {
                 // 'Else *ElseV = Else->codegen();'
                 if (ifstmt.else_branch) |else_block| {
                     for (else_block.toSlice()) |else_stmt| {
-                        try self.emitStmt(builder, &else_stmt);
+                        // keep emitting until branch has ret
+                        if (!else_rets)
+                            try self.emitStmt(builder, &else_stmt);
+
+                        switch (else_stmt) {
+                            .Return => else_rets = true,
+                            else => {},
+                        }
                     }
                 }
 
-                _ = llvm.LLVMBuildBr(builder, merge_bb);
+                if (!else_rets)
+                    _ = llvm.LLVMBuildBr(builder, merge_bb);
+
                 else_bb = llvm.LLVMGetInsertBlock(builder);
 
                 llvm.LLVMPositionBuilderAtEnd(builder, merge_bb);
 
-                var phi = llvm.LLVMBuildPhi(builder, llvm.LLVMVoidType(), c"iftmp");
+                if (then_rets and else_rets)
+                    _ = llvm.LLVMBuildUnreachable(builder);
 
-                var then_bb_val = llvm.LLVMBasicBlockAsValue(then_bb);
-                var else_bb_val = llvm.LLVMBasicBlockAsValue(else_bb);
+                // phis aren't needed since our ifs arent expressions
 
-                llvm.LLVMAddIncoming(phi, &then_bb_val, &then_bb, 1);
-                llvm.LLVMAddIncoming(phi, &else_bb_val, &else_bb, 1);
+                //var phi = llvm.LLVMBuildPhi(builder, llvm.LLVMVoidType(), c"iftmp");
+                //var then_bb_val = llvm.LLVMBasicBlockAsValue(then_bb);
+                //var else_bb_val = llvm.LLVMBasicBlockAsValue(else_bb);
+                //llvm.LLVMAddIncoming(phi, &then_bb_val, &then_bb, 1);
+                //llvm.LLVMAddIncoming(phi, &else_bb_val, &else_bb, 1);
             },
 
             else => {
@@ -250,17 +277,23 @@ pub const Codegen = struct {
         var err: ?[*]u8 = null;
         defer llvm.LLVMDisposeMessage(err);
 
-        _ = llvm.LLVMVerifyModule(
-            mod,
-            llvm.LLVMVerifierFailureAction.LLVMAbortProcessAction,
-            &err,
-        );
+        if (llvm.LLVMPrintModuleToFile(mod, c"testfile", &err) != 0) {
+            std.debug.warn("error printing module to file: {}\n", sliceify(err));
+            return CompileError.LLVMError;
+        }
 
         if (llvm.LLVMWriteBitcodeToFile(mod, c"awoo.bc") != 0) {
             std.debug.warn("error writing bitcode to file: {}\n", sliceify(err));
             return CompileError.LLVMError;
         }
 
+        std.debug.warn("cgen: verify llvm module\n");
+        _ = llvm.LLVMVerifyModule(
+            mod,
+            llvm.LLVMVerifierFailureAction.LLVMAbortProcessAction,
+            &err,
+        );
+
         llvm.LLVMInitializeAllTargetInfos();
         llvm.LLVMInitializeAllTargets();
         llvm.LLVMInitializeAllTargetMCs();
diff --git a/src/parsers.zig b/src/parsers.zig
index 900a1d1..3e0dc91 100644
--- a/src/parsers.zig
+++ b/src/parsers.zig
@@ -798,6 +798,7 @@ pub const Parser = struct {
 
     fn parseReturn(self: *@This()) !*Stmt {
         const tok = try self.consumeSingle(.Return);
+        // TODO if (self.check(.Semicolon)) insert a void literal?
         const expr = try self.parseExpr();
         return try Stmt.mkReturn(self.allocator, tok, expr);
     }